This invention relates to vessels and the like for storing hydrogen, and is especially directed to a method and apparatus for storing hydrogen in high surface area activated carbon that has been combined with a minor amount of a transition metal.
Hydrogen has become increasingly attractive as a secondary energy source as the price of petroleum increases and its availability wanes. Hydrogen is particularly interesting as a secondary fuel because it has the highest energy density per unit weight of any chemical fuel, because it can be easily produced by electrolysis of water, and because it can be used directly in a variety of energy converters from turbines and reciprocating internal combustion engines to fuel cells.
Unfortunately, hydrogen is a highly volatile fuel, and its storage in sufficient quantities has been a major stumbling block to implementation of a hydrogen-based energy storage system. Consequently, a great deal of effort has been directed towards economical storage of significant quantities of hydrogen for use as a fuel in a vehicle or in a fixed station environment.
Currently, four principal methods have been proposed for the storage of hydrogen. These include the following:
pressurization of hydrogen and storage in high-pressure vessels;
liquefaction of the hydrogen and storage at cryogenic temperatures, e.g., in a dewar vessel;
storage of the hydrogen as a metal hydride; and
cryogenic storage of the hydrogen in high surface area activated carbons.
Metal hydride storage is discussed, for example in U.S. Pat. Nos. 4,358,316 and 4,446,101, while cryogenic storage in activated carbon is discussed in C. Carpetis and W. Peschka, A Study of Hydrogen Storage by Use of Cryoadsorbents, Int. J. Hydrogen Energy, U.S. pp. 539-544, 1980.
Because energy costs of liquefying the hydrogen are avoided, cryogenic storage of hydrogen on activated carbon is considered a cost-effective storage mechanism. However, this method does have certain drawbacks, including low storage capacity per kilogram of storage medium, the need to maintain cryogenic temperatures, and the need for a pressure vessel containing the carbon storage medium to withstand high pressures, e.g., 50 to 70 atmospheres.
Consequently, there has been a strong interest in finding ways to increase the storage capacity of the material, and to store significant quantities of the hydrogen at cold, rather than cryogenic temperatures, and to store the hydrogen at pressures significantly lower than those currently employed.